Nonaqueous electrolyte secondary battery

ABSTRACT

An object of the invention is to provide a nonaqueous electrolyte secondary battery exhibiting high output characteristics in low-temperature environments, the nonaqueous electrolyte secondary battery being a lithium ion battery which uses a lithium manganese composite oxide as a positive electrode active material and a lithium titanium composite oxide as a negative electrode active material. The nonaqueous electrolyte secondary battery wherein the positive electrode active material contains a lithium-manganese composite oxide containing lithium and manganese as constituent elements, the negative electrode active material contains a lithium-titanium composite oxide containing lithium and titanium as constituent elements, and the separator contains inorganic particles is used.

RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. §371 ofInternational Application No. PCT/JP2008/003644, filed on Dec. 8, 2008,which in turn claims the benefit of Japanese Application No.2007-325039, filed on Dec. 17, 2007, the disclosures of whichApplications are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a nonaqueous electrolyte secondarybattery, and particularly to a nonaqueous electrolyte secondary batteryexhibiting high output property in low-temperature environments.

BACKGROUND ART

Lead storage batteries are widely used as back-up power sources forindustrial and business machines, and as starter power sources inautomobiles.

In recent years, there has been increasing development aimed atreplacing the lead storage batteries used as back-up power sources withnickel-hydrogen batteries and lithium-ion secondary batteries. Byreplacing lead batteries with nickel-hydrogen batteries and lithium-ionsecondary batteries, it should be possible to reduce battery sizes byachieving higher energy densities, and to reduce the environmentalburden by eliminating the need for lead.

At present, there is not a strong movement towards replacing the leadstorage batteries used as starter power sources in automobiles withnickel-hydrogen batteries or lithium-ion secondary batteries. From thestandpoint of reducing the environmental burden, however,environmentally-friendly lead-free batteries would also be desirable asstarter power sources in automobiles. Because of their lighter weight,lithium-ion secondary batteries are more promising than nickel-hydrogenbatteries for use as starter power sources in automobiles.

LiCoO₂ is known as a positive electrode active material that works in 4V-class lithium-ion secondary batteries for use as automobile starterpower sources. However, the high cost of cobalt makes it unsuited foruse in mass production of large secondary batteries such as automobilebatteries.

Moreover, since the operating voltage of a common, conventionallithium-ion battery using LiCoO₂ as the positive electrode activematerial and graphite as the negative electrode active material is 3.7V, 11.1 V is obtained with a series battery using three of this batteryand 14.8 V using four of this battery. Thus, because the operatingvoltage range of a lead storage battery is 12 V, it has not beenpossible to match an assembled battery consisting of the commonLiCoO₂-graphite lithium-ion batteries to the operating voltage range ofthe lead storage battery.

This has led to the development of a lithium-ion secondary battery inwhich a lithium-manganese composite oxide containing inexpensivemanganese in place of cobalt as a constituent element is used as thepositive electrode active material, and a lithium-titanium compositeoxide with a high reduction potential is used as the negative electrodeactive material so that the assembled battery will be compatible withthe operating range of a lead storage battery. Because the operatingvoltage of a lithium-ion secondary battery using LiCoO₂ as the positiveelectrode active material and a lithium-titanium composite oxide such asLi₄Ti₅O₁₂ for example as the negative electrode active material is 2.5V, an operating voltage of 12.5 V is obtained with a series of 5 suchbatteries, making it compatible with the operating voltage range of alead storage battery.

As an example of such a lithium-ion secondary battery, Non-patentDocument 1 discloses a lithium-ion secondary battery using alithium-manganese composite oxide with a spinel structure(Li_(1.1)Al_(0.1)Mn_(1.8)O₄) as the positive electrode active materialand a lithium-titanium composite oxide with a spinel structure(Li_(4/3)Ti_(5/3)O₄) as the negative electrode active material.

Patent Document 1 for example also discloses a positive electrode activematerial consisting of the lithium-manganese composite oxide representedby Li_(1+x)M_(y)Mn_(2−x−y)O_(4−z) (in which M is at least one selectedfrom titanium, vanadium, chromium, iron, cobalt, nickel, zinc, copper,tungsten, magnesium and aluminum; 0≦x≦0.2, 0≦y<0.5 and 0≦z<0.2), thehalf band width of the (400) diffraction peak of the composite oxideaccording to powder x-ray diffraction using CuKα radiation being atleast 0.02θ but no more than 0.1θ(θ being the diffraction angle), andthe primary particles of the composite oxide being octahedral in shape.It also proposes a battery having a positive electrode containing such apositive electrode active material and a negative electrode containingthe lithium-titanium composite oxide represented by Li_(a)Ti_(b)O₄(0.5≦a≦3, 1≦b≦2.5) as the negative electrode active material.

When the lead storage batteries used in the fields of automobile starterpower sources and back-up power sources are replaced with lithium-ionsecondary batteries and other nonaqueous electrolyte secondarybatteries, high output characteristics are required. Automobile starterpower sources in particular need to have high output characteristics inlow temperature environments because they are used also in cold regions.

The lithium-ion secondary batteries disclosed in Non-patent Document 1and in Patent Document 1, in which the lithium-manganese composite oxideis used as the positive electrode active material and thelithium-titanium composite oxide is used as the negative electrodeactive material, have had a problem that the output characteristics arelow in low temperature environments.

Non-patent Document 1: T. Ohzuku et al., Chemistry Letters, 35, 848-849(2006) Patent Document 1: Japanese Patent Application Laid-open No.2001-210324 DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a nonaqueouselectrolyte secondary battery exhibiting high output characteristics inlow-temperature environments, which is a lithium-ion secondary batteryusing a lithium-manganese composite oxide as the positive electrodeactive material and a lithium-titanium composite oxide as the negativeelectrode active material.

One aspect of the present invention is a nonaqueous electrolytesecondary battery provided with a nonaqueous electrolyte and anelectrode assembly comprising a positive electrode having a positiveelectrode active material, a negative electrode having a negativeelectrode active material, and a separator interposed between thepositive and negative electrodes, wherein the positive electrode activematerial contains a lithium-manganese composite oxide containing lithiumand manganese as constituent elements, the negative electrode activematerial contains a lithium-titanium composite oxide containing lithiumand titanium as constituent elements, and the separator containsinorganic particles.

Objects, features, aspects and advantages of the present invention willbecome more apparent by the following detailed description along withthe accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a cylindrical batterycorresponding to one embodiment of the nonaqueous electrolyte secondarybattery according to the present embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention are given below, but thepresent invention is not in any way limited by these embodiments.

As a result of exhaustive investigations studying the reasons why anonaqueous electrolyte secondary battery using a lithium-manganesecomposite oxide as the positive electrode active material and alithium-titanium composite oxide as the negative electrode activematerial exhibits poor output characteristics in low temperatureenvironments, the inventors arrived at the present invention afterfinding that the charge transfer resistance of the positive electrode ornegative electrode could be lowered by including inorganic particles inthe separator, thereby enabling to improve the output characteristics inlow-temperature environments.

The nonaqueous electrolyte secondary battery in the embodiment of thepresent invention is a nonaqueous electrolyte secondary battery providedwith a nonaqueous electrolyte and an electrode assembly comprising apositive electrode having a positive electrode active material, anegative electrode having a negative electrode active material and aseparator interposed between the positive and negative electrodes, inwhich the positive electrode active material contains alithium-manganese composite oxide containing lithium and manganese asconstituent elements, the negative electrode active material contains alithium-titanium composite oxide containing lithium and titanium asconstituent elements, and the separator contains inorganic particles.

First, the positive electrode is explained.

The positive electrode has a structure that a positive electrode mixturelayer containing the positive electrode active material is formed on thesurface of a positive electrode current collector. The positiveelectrode active material contains a lithium-manganese composite oxidecontaining lithium and manganese as constituent elements. Such apositive electrode can be obtained by a method in which a positiveelectrode mixture paste containing the positive electrode mixturedispersed in a liquid medium is coated on the positive electrode currentcollector, dried, and then rolled, or a method in which the positiveelectrode mixture is subjected to pressure bonding and then rolled, orthe like. The positive electrode mixture contains the positive electrodeactive material, a conductive agent and a binder.

The lithium-manganese composite oxide that is used as the positiveelectrode active material is not particularly limited as long as it is acomposite oxide containing lithium and manganese as constituentelements. Specific examples include composite oxides such as thoserepresented by General Formulae (1) and (2) below.

A composite oxide represented by:

Li_(1±α)[Me]O₂  (1)

(in General Formula (1), 0≦α<0.2, and Me is a transition metal includingmanganese and at least one selected from the group consisting of iron,cobalt, nickel, titanium and copper), and having a layered structure.

A composite oxide represented by:

Li_(1±α)[Me]₂O₄  (2)

(in General Formula (2), 0≦α<0.5, and Me is a transition metal includingmanganese and at least one selected from the group consisting of iron,cobalt, nickel, titanium and copper), and having a spinel structure.

In General Formulae (1) and (2) above, a is a factor that can beadjusted in order to control particle growth. That is, when the value of“1±α” is small, particle growth is suppressed during synthesis, and thesurface area tends to be large relative to the total amount of allparticles. When the value of “1±α” is large, on the other hand, particlegrowth is promoted during synthesis, and the surface area tends to besmall relative to the total amount of all particles.

The particle diameter can be controlled by adjusting the composite ratioof lithium in this way.

Among the positive electrode active material, it is particularlydesirable to contain at least one selected from the group consisting ofLi_(1±x)Ni_(1/2)Mn_(1/2)O₂ (x≦0.1), Li_(1±x)Ni_(1/3)Co_(1/3)Mn_(1/3)O₂(x≦0.1), Li_(1±x)Mn₂O₄ (x≦0.1), Li_(1, 1±x)Al_(0.1)Mn_(1.8)O₄ (x≦0.1),and Li_(1±x)Ni_(2/3)Mn_(4/3)O₄ (x≦0.1).

From the standpoint of greater safety, it is particularly desirable touse the positive electrode active material in which a part of [Me] inGeneral Formula (1) or (2) above is substituted with at least oneelement selected from the group consisting of aluminum, magnesium,strontium, calcium, yttrium, cerium and ytterbium.

Specific examples of methods for manufacturing the lithium-manganesecomposite oxide represented by General Formula (1) or (2) are givenbelow.

For example, oxides, hydroxides and/or carbonates or the like containingthe elements for constituting the positive electrode active material ofthe target composition can be mixed in specific proportions and thenbaked. With this method, however, each oxide, hydroxide and/or carbonateor the like must have a uniform particle size, and must be thoroughlymixed in order to achieve a uniform reaction.

In a different manufacturing method, a solution of lithium hydroxide orthe like is dripped into an aqueous solution of a nickel compound suchas NiSO₄.6H₂O, a cobalt compound such as CoSO₄.7H₂O, a manganesecompound such as MnSO₄.5H₂O and other transition metal compounds and thelike mixed so as to obtain an element composition for constituting thepositive electrode active material of the desired composition. After aco-precipitate is deposited as a hydroxide or a carbonate, theco-precipitate is filtered, dried, pulverized and graded to obtain thecomposite oxide. The preparation is relatively easy by this methodbecause the nickel or manganese, which is difficult to disperseuniformly, can be dispersed uniformly within the particles in advance.In the Examples described below, a lithium-manganese composite oxideco-precipitated as a hydroxide was used. Lithium hydroxide was used asthe lithium source. During baking, the reaction can also be promoted bymolding into pellets.

The positive electrode mixture layer for the positive electrodepreferably contains a conductive material for increasing the electricalconductivity of the positive electrode.

An electron conductive material that is resistant to chemical changeduring charge and discharge of a nonaqueous electrolyte secondarybattery produced by using the conductive material can be used as theconductive material, without any particular limitations. Specificexamples of such conductive materials include natural graphite (scalygraphite or the like), artificial graphite and other graphites;acetylene black, Ketjen black, channel black, furnace black, lamp black,thermal black and other carbon blacks; carbon fiber, metal fiber andother conductive fibers; carbon fluoride; copper, nickel, aluminum,silver and other metal powders; potassium titanate and other conductivewhiskers; zinc oxide, titanium oxide and other conductive metal oxides;and polyphenylene derivatives and other organic conductive materials andthe like. Any of these can be used alone, or two or more can be used incombination. Of these, artificial graphite, acetylene black and nickelpowder are particular desirable.

The compounding proportion of the conductive material is notparticularly limited, but it is preferably 1 to 50 mass % or morepreferably 1 to 30 mass % of the positive electrode mixture layer. 2 to15 mass % is particularly desirable when graphite or carbon black isused.

A binder is also included in the positive electrode mixture layer. Thebinder is preferably one that is resistant to chemical change duringcharge and discharge when used in a nonaqueous electrolyte secondarybattery. Consequently, a polymer with a decomposition-startingtemperature of 200° C. or more is preferred. Specific examples of suchbinders include polyethylene (PE), polypropylene (PP),polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF),tetrafluoroethylene-hexafluoroethylene copolymer,tetrafluoroethylene-hexafluoropropylene copolymer (FEP),tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA),vinylidene fluoride-hexafluoropropylene copolymer, vinylidenefluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylenecopolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidenefluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylenecopolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE),vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer,vinylidene fluoride-perfluoromethylvinyl ether-tetrafluoroethylenecopolymer and the like. Any of these can be used alone, or two or morecan be used in combination. Of these, polyvinylidene fluoride (PVDF) andpolytetrafluoroethylene (PTFE) are preferred.

Any electron conductor that is resistant to chemical change duringcharge and discharge when used in a nonaqueous electrolyte secondarybattery can be used for the positive electrode current collector,without any particular limitations. Specific examples of materials forthe positive electrode current collector include stainless steel,nickel, aluminum, titanium, various alloys, carbon and the like, as wellas composite materials that aluminum or stainless steel has beensurface-treated with carbon, nickel, titanium, silver or the like. Thesurfaces of these materials may have been subjected to an oxidationtreatment or a treatment to give an irregular surface. In the presentembodiment, as explained below, it is especially desirable to usealuminum or an aluminum alloy and other aluminum-based metal for thepositive electrode current collector and a negative electrode currentcollector.

The form of the positive electrode current collector is not particularlylimited as long as it is a form that is conventionally used innonaqueous electrolyte secondary batteries. Specific examples of suchforms include foils, films, sheets, nets, punched forms, lath materials,porous materials, foams, fiber groups, nonwoven fabrics and the like.The thickness of the positive electrode current collector is notparticularly limited but is preferably 1 to 500 μm for example.

Next, the negative electrode is explained.

For the negative electrode, a negative electrode mixture layercontaining the negative electrode active material is formed on thesurface of a negative electrode current collector. The negativeelectrode active material contains a lithium-titanium composite oxidecontaining lithium and titanium as constituent elements. Such a negativeelectrode can be obtained by a method in which the negative electrodeactive material, a binder and a conductive material as necessary aredissolved or dispersed in a liquid medium to obtain a slurry, which isthen kneaded to obtain a paste for the negative electrode mixture layerthat is coated on the surface of the negative electrode currentcollector, dried, and rolled, or a method in which the negativeelectrode mixture is press-bonded and then rolled.

The lithium-titanium composite oxide used as the negative electrodeactive material is not particularly limited as long as it is a compositeoxide containing lithium and titanium as constituent elements, but alithium-titanium composite oxide having a spinel structure isparticularly desirable.

Specific examples of lithium-titanium composite oxides includeLi₄Ti₅O₁₂, Li_(x)TiO₂ (0<x≦0.8) and the like. Of these, Li₄Ti₅O₁₂ isespecially desirable.

Li₄Ti₅O₁₂ is a negative electrode active material used in commerciallithium-ion secondary batteries, and high-quality Li₄Ti₅O₁₂ is availableas a commercial product. It can also be synthesized by mixing lithiumcarbonate, lithium hydroxide or another lithium compound with titaniumoxide as the titanium source to obtain the target composition, and thenbaking at a temperature of about 800° C. to 1100° C. in air or an oxygenstream or other oxidation atmosphere.

A conductive material can be compounded as necessary in the negativeelectrode mixture layer in order to improve the conductivity of thenegative electrode. Conductive materials similar to those used in thepositive electrode can be used. The compounded proportion of theconductive material is not particularly limited but is normally 0 to 10mass % or preferably 0 to 5 mass % of the negative electrode mixturelayer.

The negative electrode mixture layer also contains a binder. In additionto the binders compounded in the positive electrode mixture layer,styrene-butadiene rubber (SBR) and other rubber binders also can bepreferably used.

An electron conductive material that is resistant to chemical changeduring charge and discharge when used in a nonaqueous electrolytesecondary battery can be used for the negative electrode currentcollector, without any particular limitations. Specific examples ofmaterials for the negative electrode current collector include aluminum,aluminum-based metals such as Al—Cd alloys and other aluminum alloys,stainless steel, nickel, copper, titanium and carbon as well as copperor stainless steel that has been surface-treated with carbon, nickel,titanium or silver or the like. The surfaces of these materials may alsobe oxidative-treated or treated to give an irregular surface.

The form of the negative electrode current collector is not particularlylimited as long as it is one that is conventionally used in the negativeelectrodes of nonaqueous electrolyte secondary batteries. Specificexamples include foils, films, sheets, nets, punched forms, rathmaterials, porous materials, foams, fiber groups, nonwoven fabrics andthe like. The thickness of the negative electrode is not particularlylimited but is preferably 1 to 500 μm for example.

In the nonaqueous electrolyte secondary battery of the presentembodiment, it is desirable that both the positive electrode currentcollector and negative electrode current collector comprises thealuminum-based metal. Using the aluminum-based metal also allows theweight and cost of the battery to be reduced compared to a case usingcopper and the like, which are commonly used as negative electrodecurrent collector materials in lithium-ion secondary battery.

In a lithium-ion secondary battery using graphite as the negativeelectrode active material, which has a low potential of 0.2 V or lesswith respect to the lithium metal, it has not been possible to use thealuminum-based metal for a current collector. This is because thealuminum-based metal initiates a reaction with the lithium ions at apotential higher than the charge-discharge potential of the graphite inthe negative electrode. In contrast, in a nonaqueous electrolytesecondary battery using a lithium-titanium composite oxide as thenegative electrode active material, because the charge-dischargepotential of the negative electrode is as high as 1.55 V, it is possibleto use the aluminum-based metal for the current collector, which reactsat a potential lower than this potential.

When copper is used for the negative electrode current collector,moreover, the phenomenon of copper ion elution into the nonaqueouselectrolyte occurs when the potential of the negative electrode risesdue to deep discharge. When this occurs, copper is precipitated on thenegative electrode surface prior to the insertion reaction of thelithium during recharging, thus inhibiting the lithium insertionreaction. In this case, lithium is precipitated on the negativeelectrode surface in the form of needle-shaped crystals. This reducesthe safety of the battery, and can be a cause of reduced cycle life.When aluminum is used for the negative electrode current collector, onthe other hand, the elution or re-precipitation of the metal ions doesnot occur.

Further, there is the risk that if a battery charger breaks down when anegative electrode-limited battery is connected to the charger, excesslithium will be supplied to the negative electrode due to overchargingof the battery. In this case, when copper is used for the negativeelectrode current collector, excess lithium metal is precipitated in theform of needle-shaped crystals on the negative electrode surface. Theseneedle-shaped crystals of lithium metal reduce the safety of the batteryagainst overcharge. When the aluminum-based metal is used for thenegative electrode current collector, on the other hand, becausealuminum has a strong ability to absorb and store lithium, the lithiummetal is not precipitated on the negative electrode surface but absorbedand stored on the current collector during overcharge. Consequently,using the aluminum-based metal for the negative electrode currentcollector can provide the current collector with a safety functionagainst battery overcharge.

The positive electrode and negative electrode were described above, butthe positive and negative electrodes are not limited to theseconfigurations. For example, an underlayer could be interposed betweenthe current collector and the mixture layer with the aim of improvingadhesiveness between the current collector and the mixture layer,conductivity, cycle characteristics and charging/discharging efficiency,or a protective layer could be formed on the surface of the mixturelayer to mechanically or chemically protect the mixture layer. Theunderlayer and mixture layer can contain, for example, binders,conductive particles, non-conductive inorganic particles and the like.

Next, the separator is explained.

The separator which is a porous thin film, a woven fabric or a nonwovenfabric or the like can be used without any particular limitations, aslong as it has sufficient ion permeability, mechanical strength andinsulating properties for use as a separator in a nonaqueous electrolytesecondary battery and it contains inorganic particles.

The separator may be a single layer of a single material, or may be alaminate of multiple layers such as a porous resin layer for providing ashut-down function. “Shut-down function” means the function ofcontrolling Joule heat generation and the like by blocking through-holesin the porous resin thin film by thermal fusion to thereby prevent ionconduction when the battery becomes hot during charge and discharge.

One example of a method for manufacturing such a separator containingthe inorganic particles is explained below.

First, a resin for forming the separator is dissolved in an organicsolvent to prepare a resin solution. A water-soluble powder such aslithium chloride powder is dissolved with agitation in the resultingresin solution, and the inorganic particles are added with agitation toobtain a dispersion liquid of the inorganic particles. The resultingdispersion liquid of inorganic particles is applied to a substrate so asto have a specific thickness, and dried to form a thin film. Theresulting thin film is dipped in a warm bath to dissolve and removelithium chloride and other water-soluble material in the thin film andthereby to form fine pores, and then washed in water to form a porousthin film containing the inorganic particles.

Specific examples of resins for forming the separator includepolypropylene, polyethylene and other polyolefin resins, and polyimide,polyamidimide, aramide, and polyphenylene sulfide, or polyetherimide,polyethylene terephthalate, polyether nitrile, polyether etherketone,polybenzimidazole and other heat-resistant resins with a deflectiontemperature under load of 200° C. or more. The aforementioned polyolefinresins are desirable since they have excellent durability and providethe shut-down function. The aforementioned heat-resistant resins arepreferable from the standpoint of safety against internal short-circuit.The deflection temperature under load is the temperature as measured at1.82 MPa by ASTM-D648.

The thickness of the separator formed in this way is 10 to 300 μm orpreferably 10 to 40 μm or more preferably 10 to 30 μm or especially 15to 25 μm.

The following method is an example of a different manufacturing method.A paste containing specific amounts of a binder, the inorganic particlesand an organic solvent is coated on the surface of a positive electrodeplate or negative electrode plate, and the solvent is removed by dryingto form fine pores. In this method, a porous thin film containing theinorganic particles, which is adhesively laminated on the surface of thepositive electrode or negative electrode, is formed. The separatorobtained by such a manufacturing method is desirable from the standpointof excellent shape stability. The binder is a component that allows theinorganic particles to bind one another and ensures the flexibility ofthe separator.

In this method, the percentage content of the binder in the separator ispreferably about 1 to 50 mass %. If the binder content is too high, thepores composed of gaps between the inorganic particles decrease inamount, and if the binder content is too low, the inorganic particlesmay even fall out because of insufficient adhesive force binding themtogether.

Examples of the binder include commonly used polyethylene (PE),polypropylene (PP), polytetrafluoroethylene (PTFE), polyvinylidenefluoride (PVDF), styrene-butadiene rubber (SBR), and rubber polymerscontaining polyacrylonitrile units and the like. Considering the safetyof the nonaqueous electrolyte secondary battery in particular, a rubberpolymer containing polyacrylonitrile units, which has adecomposition-starting temperature of 200° C. or more and has rubberelasticity to maintain the flexibility of the electrode plate, can beused by preference.

The thickness of the separator formed in this way is preferably 1 to 35μm or more preferably 3 to 25 μm.

In an another manufacturing method, a paste containing specificquantities of a binder, the inorganic particles and an organic solventis coated on the surface of a woven fabric or a nonwoven fabric, and thesolvent is removed by drying to form fine pores, thus providing a porousthin film containing the inorganic particles.

As the nonwoven fabric, the fabric having an average pore diameter of0.1 μm or more, in which the diameter of the fibers making up thenonwoven cloth is about 1 to 3 μm, is preferable from the standpoint ofthe battery characteristics. The fabric or the like in which the fibersare partially fused together by heated calender roll treatment isdesirable since it is effective in providing thinness and increasedstrength.

In an another manufacturing method, a resin already made to contain theinorganic particles is melt blown to obtain a nonwoven fabric formedfrom fibers containing the inorganic particles.

In an another manufacturing method, a suitable quantity of the inorganicparticles is scattered on the surface of a porous thin film, a wovenfabric or a nonwoven fabric each having previously-formed fine pores,and this is pressed at a temperature sufficient to soften theconstituent resin so that the inorganic particles are press bonded.After press bonding the inorganic particles, in order to remove unbondedinorganic particles, a flow of air is blown over the separator, or theseparator is immersed in a liquid for ultrasonic cleaning. Thus, theseparator containing the inorganic particles is formed.

As the inorganic particles, a material that has the effect of adsorbingmanganese ions and that is resistant to chemical change during chargeand discharge when used in a nonaqueous electrolyte secondary batterycan be used, without any particular limitations. Desirable examplesinclude alumina, magnesia, titania, zirconia, silica and other inorganicoxide particles, and glass powder, mica whiskers, ceramic fine powderand the like. Of these, alumina, magnesia, titania, zirconia, silica andother inorganic oxide particles are preferred, and alumina, magnesia andsilica are especially preferred because of their strong ability toadsorb manganese ions. One kind of the inorganic particles can be used,or two or more kinds can be used in combination.

Regarding the average particle size of the inorganic particles, themedian diameter is preferably 0.1 to 5 μm or more preferably 0.2 to 1.5μm from the standpoint of shape stability and ionic conductivity of theseparator. If the median diameter is too large, ionic conductivity willtend to decline, while if it is too small, adhesiveness between theinorganic particles will decline, and it may be hard to obtainsufficient shape stability. For purposes of forming a dense porous thinfilm, it is desirable to use a mixture of the inorganic particles of thesame kind but with different median diameters.

The percentage content of the organic particles in the separator shouldbe 0.1 to 99 mass % or preferably 25 to 75 mass % for purposes ofachieving a satisfactory effect of adsorbing manganese ions.

The porosity of the separator is preferably in the range of 30 to 70% ormore preferably 35 to 60% from the standpoint of ensuring adequate ionicconductivity. Here, the porosity is the volume ratio of pores relativeto the separator volume.

Next, the nonaqueous electrolyte is explained.

A nonaqueous electrolytic solution or a solid electrolyte that is widelyused as a nonaqueous electrolyte in conventional lithium-ion secondarybatteries can be used as the nonaqueous electrolyte. In particular, inthe nonaqueous electrolyte secondary battery of the present embodiment,since the lithium-manganese composite oxide is used as the positiveelectrode active material and the lithium-titanium composite oxide isused as the negative electrode active material, a broader selection ofthe nonaqueous electrolytes is possible as discussed below.

The nonaqueous electrolytic solution is composed of an organic solventand a lithium salt or other solute dissolved in the organic solvent.

As the organic solvent for use in the nonaqueous electrolytic solution,a nonaqueous solvent conventionally used for lithium-ion secondarybatteries can be used, without any particular limitations. Specificexamples of the organic solvents include ethylene carbonate (EC),propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate(VC) and other cyclic carbonates; γ-butyrolactone (GBL) and other cycliccarboxylic acid esters; dimethyl carbonate (DMC), diethyl carbonate(DEC), ethylmethyl carbonate (EMC), dipropyl carbonate (DPC) and otheracyclic carbonates; methyl formate (MF), methyl acetate (MA), methylpropionate (MP), ethyl propionate (MA) and other aliphatic carboxylicacid esters; mixed solvents containing cyclic carbonates and acycliccarbonates; mixed solvents containing cyclic carboxylic acid esters; andmixed solvents containing cyclic carboxylic acid esters and cycliccarbonates and the like. The aliphatic carboxylic acid ester ispreferably included in the range of 30% or less or more preferably 20%or less of the total solvent weight.

In the nonaqueous electrolyte secondary battery of the presentembodiment, an organic solvent with a narrow potential window can bepreferably used as explained below because the lithium-manganesecomposite oxide is used as the positive electrode active material andthe lithium-titanium composite oxide is used as the negative electrodepositive material. In a common, conventional lithium-ion battery using anegative electrode active material consisting of a carbon material, itwas difficult to use the organic solvent with a narrow potential window.

An organic solvent used in the nonaqueous electrolytic solution has apotential window. The potential window is a measure of oxidationresistance and reduction resistance, and it can be said that the widerthe potential window is, the more stable the organic solvent is.

In a common, conventional lithium-ion secondary battery using lithiumcobaltate as the positive electrode active material and a carbonmaterial as the negative electrode active material, oxidation resistanceuntil near 4.25 V (the charge-discharge potential of cobalt) andreduction resistance until near 0 V (the charge-discharge potential ofgraphite) are required. Here and below, the potential is based onlithium metal. Consequently, in a common, conventional lithium-ionsecondary battery, it was difficult to use an organic solvent in whichits potential window does not include near 4.25 V and near 0 V.

Examples of the organic solvents that do not include near 4.25 V andnear 0 V in their potential windows include organic solvents of lactonesand propylene carbonate. These solvents are useful because they areinexpensive, have good ability to dissolve electrolytes because of theirlarge dielectric constants, and also have excellent oxidationresistance. Further, trimethylphosphate (TMP) and triethylphosphate(TEP) are organic solvents that are very safe because of theirfire-extinguishing effects, but were difficult to use because of theirlow reduction resistance. Such organic solvents were difficult to use inthe lithium-ion secondary batteries using graphite as the negativeelectrode active material because they have low reduction resistance andare decomposed during charge and discharge of the graphite.

For example, in a nonaqueous electrolyte secondary battery usingLi₄Ti₅O₁₂ (Li[Li_(1/3)Ti_(5/3)]O₄) as the negative electrode, thenegative electrode potential is 1.55 V. Consequently, the level ofreduction resistance required for the organic solvent is much morealleviated. As a result, the decomposition of propylene carbonate orother solvent on the negative electrode surface which was caused duringcharge and discharge of the lithium-ion secondary battery using graphitedoes not occur. In this way, the organic solvent with a narrow potentialwindow as described above can be used in the nonaqueous electrolytesecondary battery of the present invention because the lithium-titaniumcomposite oxide is used as the negative electrode active material.

When the composite oxide containing lithium and manganese as constituentelements is used for the positive electrode, moreover, the potential ofthe positive electrode rises to about 4.55 V or more, but this is not aproblem in using the organic solvents described above because theoxidation resistance of each of the organic solvents described above is5 V or more. It is thought that the highly oxidation-resistant solventssuch as sulfolane (SL), methyl diglyme, acetonitrile (AN), propionitrile(PN), butyronitrile (BN),1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TFETFPE),2,2,3,3-tetrafluoropropyldifluoromethyl ether (TFPDFME), methyldifluoroacetate (MDFA), ethyl difluoroacetate (EDFA), fluorinatedethylene carbonate are also appropriate. The conventionally usedsolvents such as dimethyl carbonate (DMC), methylethyl carbonate (MEC)and diethyl carbonate (DEC) can also be used to dilute highly viscoussolvents.

EC is a desirable organic solvent because of its large dielectricconstant and high liquid stability. Fluorinated EC obtained byfluorinating the hydrogen of EC is desirable for its high oxidationresistance. Compared to EC, fluorinated EC is considered useful becauseit can suppress generation of CO₂ gas, which is thought to be caused bydecomposition of EC on the positive electrode surface during batterystorage at a high temperature. However, in a lithium-ion secondarybattery using a carbon material for the negative electrode activematerial, fluorinated EC is difficult to use because it undergoesreductive degradation. In the secondary battery of the presentembodiment, fluorinated EC can be used because the lithium-titaniumcomposite oxide is used for the negative electrode active material.

As explained above, in the nonaqueous electrolyte secondary batteryusing the lithium-titanium composite oxide as the negative electrodeactive material, the organic solvents can be selected from a much widerrange than in a conventional nonaqueous electrolyte secondary battery.

As a solute for use in the nonaqueous electrolytic solution, Lithiumsalts of inorganic anions and lithium salts of organic anions and thelike that are conventionally used as electrolytes in lithium-ionsecondary batteries can be used, without any particular limitations.Specific examples include LiClO₄, LiBF₄, LiPF₆, LiAlCl₄, LiSbF₆, LiSCN,LiCF₃SO₃, LiCF₃CO₂, LiCF₃SO₂, LiAsF₆, LiB₁₀Cl₁₀, lower aliphatic lithiumcarboxylate, chloroborane lithium, lithium tetraphenylborate,LiN(CF₃SO₂)(C₂F₅SO₂), LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂, LiN(CF₃SO₂)(C₄F₉SO₂)and other imides. Each of these can be used alone, or two or more can beused in combination. Of these, the solute containing LiPF₆ can be usedby preference.

The dissolved amount of the lithium salt in the nonaqueous solvent isnot particular limited, but is preferably 0.2 to 2 mol/liter.

The added amount of the nonaqueous electrolytic solution is notparticularly limited, and can be adjusted appropriately according to thesize of the battery and the amounts of the positive electrode activematerial and negative electrode active material.

A solid electrolyte can also be used in the nonaqueous electrolytesecondary battery. In the nonaqueous electrolyte secondary battery ofthe present embodiment, there is little volume expansion of the positiveand negative electrodes. Consequently, it is possible to control theproblem caused in using solid electrolytes that peeling at the boundarybetween the electrode plate and the solid electrolyte occurs due toexpansion and shrinkage of the electrode plate.

The solid electrolytes are classified as inorganic solid electrolytes ororganic solid electrolytes.

Examples of the inorganic solid electrolytes include Li nitrides,halides, oxo-acid salts and the like. In particular, 80Li₂S-20P₂O₅, theamorphous Li₃PO₄-63Li₂S-36SiS₂, 44LiI-38Li₂S-18P₂S₅ and other sulfides,Li_(2.9)PO_(3.3)N_(0.46) oxide and Li_(3.25)Ge_(0.25)P_(0.75)S₄ sulfideas an amorphous substance, and La_(0.56)Li_(0.33)TiO₃ andLi_(1.4)Al_(0.3)Ti_(1.6)(PO₄)₃ oxides and the like can be used bypreference. It is also desirable to use a method in which a mixedsintered material of LiF and LiBO₂ is used to achieve sintering of eachmaterial while simultaneously forming a solid electrolyte layer at abonded interface, or the like.

Specific examples of the organic solid electrolytes include polymermaterials such as polyethylene oxide, polypropylene oxide,polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol,polyvinylidene fluoride, polyhexafluoropropylene and derivatives,mixtures and composites of these. These may be used alone, or two ormore may be used in combination. Of these, a copolymer of vinylidenefluoride and hexafluoropropylene or a mixture of vinylidene polyfluorideand polyethylene oxide can be used by preference. A gel electrolytecontaining the organic solid electrolyte and a nonaqeuous electrolyticsolution can also be used by preference.

Next, the configuration of the nonaqueous electrolyte secondary batteryis explained.

FIG. 1 shows a partial cross-sectional view of a cylindrical batterycorresponding to one embodiment of the nonaqueous electrolyte secondarybattery. In the cylindrical battery shown in FIG. 1, battery case 1contains electrode plate assembly 4, which is obtained by winding thepositive and negative electrodes multiple times in a spiral form with aseparator between them. Positive electrode lead 5 led from the positiveelectrode is connected to seal plate 2, while negative electrode lead 6led from the negative electrode is connected to the bottom of batterycase 1. An electron conducting metal or alloy that is resistant toorganic electrolytic solutions is used for the battery case and the leadplates. Specifically, iron, nickel, titanium, chromium, molybdenum,copper, aluminum and other metals or alloys of these metals can be used.A stainless steel plate or Al—Mn alloy plate is preferably worked forthe battery case, and aluminum is desirable for the positive electrodelead. Nickel or aluminum is preferred as the material of the negativeelectrode lead. For the battery case, various engineering plastics andcombinations of metals with various engineering plastics can also beused to reduce its weight.

Electrode plate assembly 4 is provided with insulating rings 7 each atthe top and bottom. The electrolytic solution is injected, and thebattery case is sealed with gasket 3 using the seal plate. The sealplate can also be provided with a safety valve.

Various conventionally known safety elements can also be used, such asfuses, bimetals, PTC elements and the like for preventing overcurrent.In addition to a safety valve, measures that can be used to preventincreased pressure inside the battery case include making a notch in thecase, cracking the gasket, cracking the seal plate and disconnecting thelead plate. A protective circuit that incorporates means againstovercharge and overdischarge can be provided as part of the batterycharger, or can be connected independently. For welding the caps,battery case, sheets and leads, a known method (such as AC or DCelectrical welding, laser welding or ultrasound welding) can be used. Asthe seal material, a conventionally known compound or mixture such asasphalt or the like can be used.

The battery may be in any shape such as a coin, button, sheet, cylinder,flat shape, angular shape or the like. If the battery shape is acoin-type or a button-type, the positive electrode mixture and negativeelectrode mixture are generally compressed into pellet shape forpurposes of use. The thickness and diameter of the pellets can bedetermined by the size of the battery. A shape of the wound electrodeassembly in the present invention is not necessarily a true cylinder,and may be a flattened cylinder with an oval cross-section or aprismatic shape with an oblong cross-section.

Hereinafter, the present invention is explained in more detail by meansof examples. However, the present invention is not in any way limited bythese examples.

EXAMPLES

First, the manufacture of Sample Batteries 1A through 9T used in thepresent embodiment and Comparative Batteries 1U through 11Z isexplained.

<Sample Battery 1A>

(Preparation of Positive Electrode Plate)

3 kg of Li_(1.1)Al_(0.1)Mn_(1.8)O₄, 1.5 kg of PVDF solution (solids 12mass % in N-methylpyrrolidone (NMP) solution, Kureha Corp. #1320), 120 gof acetylene black and a suitable amount of NMP were agitated with adual-arm kneader to prepare a positive electrode mixture layer paste.The resulting positive electrode mixture layer paste was coated on bothsides of a current collector consisting of 20 μm-thick aluminum foil,dried, and rolled to a total thickness of 160 μm to form a laminate of acurrent collector with positive electrode mixture layers. The resultinglaminate was cut to a width suited to insertion into a cylindrical 18650battery case to obtain the positive electrode plate.

(Preparation of Negative Electrode Plate)

3 kg of Li₄Ti₅O₁₂, 1.5 kg of the aforementioned PVDF solution, 120 g ofacetylene black and a suitable amount of NMP were agitated with adual-arm kneader to prepare a negative electrode mixture layer paste.The resulting negative electrode mixture layer paste was coated on bothsides of a current collector consisting of 20 μm-thick aluminum foil,dried, and rolled to a total thickness of 140 μm to form a laminate of acurrent collector with negative electrode mixture layers. The resultinglaminate was cut to a width suited to insertion into a cylindrical 18650battery case to obtain the negative electrode plate.

(Preparation of Aluminum Particle-Containing Porous Aramide Thin Film)

200 g of aramide resin fiber (3 mm cut fiber, deflection temperatureunder load 320° C. or more, Toray Dupont KEVLAR) was dissolved at 80° C.in 800 g of N-methylpyrrolidone to obtain a resin solution. 10 g oflithium chloride powder (Kanto Chemical) was dissolved with agitation inthe resulting resin solution, and 0.2 g (0.1 mass % of the resincomponent) of alumina powder (median diameter 0.3 μm) was added withthorough agitation to obtain an alumina particle dispersion. Thisalumina particle dispersion was applied with a bar coater having a 200pm thick gap to a glass substrate heated to 60° C., and dried for 3hours in a 110° C. drying oven to obtain a white thin film. This thinfilm was immersed for 2.5 hours in a warm water bath of distilled waterat 60° C. to dissolve the lithium chloride in the thin film. This thinfilm was then washed with pure water to obtain an aluminaparticle-containing porous aramide thin film. The thickness of theresulting alumina particle-containing porous aramide thin film was 30μm.

(Assembly of Nonaqueous Electrolyte Secondary Battery)

Leads were ultrasound welded to both the positive electrode plate andnegative electrode plate. The positive electrode plate and negativeelectrode plate were laminated with the inorganic particle-containingporous aramide thin film (separator) in between, wound, and cut to aspecific length to obtain an electrode assembly. This electrode assemblywas then placed in a cylindrical 18650 battery case, and 5 g of anonaqueous electrolytic solution containing 1.5 M LiPF₆ dissolved in anEC/MEC mixed solvent (volume ratio 1:3) was added. The battery case wasthen sealed to obtain a cylindrical 18650 lithium-ion secondary battery.This was called Sample Battery 1A.

<Sample Battery 2A>

970 g of alumina powder (median diameter 0.3 μm), 375 g of ZeonCorporation's polyacrylonitrile rubber binder BM-720H (solids 8 weight%) and a suitable amount of NMP were agitated with a dual-arm kneader toprepare a porous thin film layer paste. The porous thin film layer pastewas coated to a thickness of 30 μm on both sides of a positive electrodeplate similar to that used in Sample Battery 1A, and dried to adhesivelylaminate porous thin film layers on the surfaces of the positiveelectrode plate. The porous thin film layer functions as a separator.

Leads were then welded to the positive plate with the porous thin filmlayers formed thereon and a negative plate similar to that used inSample Battery 1A. The positive and negative plates were then laminatedtogether, wound, and cut to a prescribed length to obtain an electrodeassembly. A secondary battery was then obtained by the same methods usedto prepare Sample Battery 1A using the resulting electrode assembly.This was called Sample Battery 2A.

<Sample Battery 3A>

A secondary battery was obtained by the same methods used to prepareSample Battery 2A except that porous thin film layers were formed on thesurface of the negative electrode plate rather than on the positiveelectrode plate. This was called Sample Battery 3A.

<Sample Battery 4A>

A 5 μm-thick alumina particle-containing porous aramide thin film wasprepared as in Sample Battery 1A except that the thickness of thealumina particle-containing porous aramide thin film was different.

25 μm-thick polyethylene-polypropylene composite film with a shut-downfunction (Celgard 2300, shut-down temperature 120° C., hereunder calledPE/PP thin film) was laid as a shut-down layer over one side of theresulting alumina particle-containing porous aramide thin film, andpress bonded with a hot roll press heated to 90° C. to prepare a 30μm-thick separator consisting of a shut-down layer laminated with analumina particle-containing porous aramide thin film.

A secondary battery was obtained by the same methods used to prepareSample Battery 1A except that this separator was used instead of theseparator used in Sample Battery 1A. This was called Sample Battery 4A.

<Sample Batteries 5A and 6A>

Secondary batteries were prepared by the same methods used to prepareSample Batteries 2A and 3A, respectively, except that the positive andnegative plates were wound with PE/PP thin film between the plates inthe battery assembly process. These were called Sample Batteries 5A and6A, respectively.

<Sample Batteries 7A and 8A>

Secondary batteries were obtained by the same methods used to prepareSample Batteries 5A and 6A, respectively, except that 30 μm-thicknonwoven fabric consisting of polypropylene fiber (average pore size 0.3μm, fiber diameter 2 μm, hereunder optionally called “PP nonwoven”) wasused instead of the PE/PP thin film. These were called Sample Batteries7A and 8A, respectively.

<Sample Battery 9A>

A secondary battery was obtained by the same methods used to prepareSample Battery 1A except that the alumina particle-containingpolypropylene nonwoven fabric described below was used in place of thealumina particle-containing porous aramide thin film. This was calledSample Battery 9A. The alumina particle-containing polypropylene nowovenfabric was prepared as follows.

The porous thin film layer paste used in manufacturing Sample Battery 2Awas applied to 5 μm on both sides of 25 μm-thick nonwoven fabricconsisting of polypropylene fibers (average pore size 0.7 μm, fiberdiameter 2 μm) to impregnate the cloth, and then dried to obtain aluminaparticle-containing polypropylene nonwoven fabric. The alumina contentof the resulting alumina particle-containing polypropylene nonwovenfabric as determined by ICP emission spectrometry was 0.5 mass %.

<Sample Battery 10A>

A secondary battery was obtained by the same methods used to prepareSample Battery 1A except that 0.1 g (0.05 mass %) of alumina powder wasadded instead of 0.2 g (0.1 mass %) of alumina powder to prepare thealumina particle-containing porous aramide thin film. This was calledSample Battery 10A.

<Sample Batteries 1B through 9B>

Sample Batteries 1B through 9B were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except thatLiNi_(1/2)Mn_(1/2)O₂ was used as the positive electrode active material.

<Sample Batteries 1C through 9C>

Sample Batteries 1C through 9C were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except thatLiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ was used as the positive electrode activematerial.

<Sample Batteries 1D through 9D>

Sample Batteries 1D through 9D were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except thatLi_(1.1)Mn₂O₄ was used as the positive electrode active material.

<Sample Batteries 1E through 9E>

Sample Batteries 1E through 9E were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except thatLiNi_(2/3)Mn_(4/3)O₄ was used as the positive electrode active material.

<Sample Batteries 1F through 9F>

Sample Batteries 1F through 9F were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except that anonaqueous electrolytic solution containing 1.5 M LiPF₆ dissolved in aPC/MEC mixed solvent (volume ratio 1:1) was used in place of thenonaqueous electrolytic solution containing 1.5 M LiPF₆ dissolved in anEC/MEC mixed solvent.

<Sample Batteries 1G through 9G>

Sample Batteries 1G through 9G were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except that anonaqueous electrolytic solution containing 1.5 M LiPF₆ dissolved in TMPsolvent was used in place of the nonaqueous electrolytic solutioncontaining 1.5 M LiPF₆ dissolved in an EC/MEC mixed solvent.

<Sample Batteries 1H through 9H>

Sample Batteries 1H through 9H were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except that anonaqueous electrolytic solution containing 1.5 M LiPF₆ dissolved in SLwas used in place of the nonaqueous electrolytic solution containing 1.5M LiPF₆ dissolved in an EC/MEC mixed solvent.

<Sample Batteries 1I through 9I>

Sample Batteries 1I through 9I were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except that anonaqueous electrolytic solution containing 1.5 M LiPF₆ dissolved in ANwas used in place of the nonaqueous electrolytic solution containing 1.5M LiPF₆ dissolved in an EC/MEC mixed solvent.

<Sample Batteries 1J through 9J>

Sample Batteries 1J through 9J were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except that anonaqueous electrolytic solution containing 1.5 M LiPF₆ dissolved in PNwas used in place of the nonaqueous electrolytic solution containing 1.5M LiPF₆ dissolved in an EC/MEC mixed solvent.

<Sample Batteries 1K through 9K>

Sample Batteries 1K through 9K were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except that anonaqueous electrolytic solution containing 1.5 M LiPF₆ dissolved in BNwas used in place of the nonaqueous electrolytic solution containing 1.5M LiPF₆ dissolved in an EC/MEC mixed solvent.

<Sample Batteries 1L through 9L>

Sample Batteries 1L through 9L were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except that anonaqueous electrolytic solution containing 1.5 M LiPF₆ dissolved inTFETFPE was used in place of the nonaqueous electrolytic solutioncontaining 1.5 M LiPF₆ dissolved in an EC/MEC mixed solvent.

<Sample Batteries 1M through 9M>

Sample Batteries 1M through 9M were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except that anonaqueous electrolytic solution containing 1.5 M LiPF₆ dissolved inTFPDFME was used in place of the nonaqueous electrolytic solutioncontaining 1.5 M LiPF₆ dissolved in an EC/MEC mixed solvent.

<Sample Batteries 1N through 9N>

Sample Batteries 1N through 9N were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except that anonaqueous electrolytic solution containing 1.5 M LiPF₆ dissolved inMDFA was used in place of the nonaqueous electrolytic solutioncontaining 1.5 M LiPF₆ dissolved in an EC/MEC mixed solvent.

<Sample Batteries 1O through 9O>

Sample Batteries 1O through 9O were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except that anonaqueous electrolytic solution containing 1.5 M LiPF₆ dissolved inEDFA was used in place of the nonaqueous electrolytic solutioncontaining 1.5 M LiPF₆ dissolved in an EC/MEC mixed solvent.

<Sample Batteries 1P through 9P>

Sample Batteries 1P through 9P were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except that anonaqueous electrolytic solution containing 1.5 M LiPF₆ dissolved inETFEC (ethyl 2,2,2-trifluoroethyl carbonate) was used in place of thenonaqueous electrolytic solution containing 1.5 M LiPF₆ dissolved in anEC/MEC mixed solvent.

<Sample Batteries 1Q through 9Q>

Sample Batteries 1Q through 9Q were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except that anonaqueous electrolytic solution containing 1.5 M LiPF₆ dissolved inDTFEC (di-(2,2,2-trifluoroethyl)carbonate) was used in place of thenonaqueous electrolytic solution containing 1.5 M LiPF₆ dissolved in anEC/MEC mixed solvent.

<Sample Batteries 1R through 9R>

Sample Batteries 1R through 9R were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except thatmagnesia powder (median diameter 0.3 μm) was used in place of thealumina powder (median diameter 0.3 μm).

<Sample Batteries 1S through 9S>

Sample Batteries 1S through 9S were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except that glassfiber (ZP150 from Asahi Fiber Glass) was used in place of the aluminapowder (median diameter 0.3 μm).

<Sample Batteries 1T through 9T>

Sample Batteries 1T through 9T were obtained by the same methods used toprepare Sample Batteries 1A through 9A, respectively, except that micawhiskers (median diameter 0.3 μm) were used in place of the aluminapowder (median diameter 0.3 μm).

<Comparative Batteries 1U and 1V>

Comparative Batteries 1U and 1V were obtained by the same methods usedto prepare Sample Batteries 1A and 1E, respectively, except that noalumina was added when preparing the alumina particle-containing porousaramide thin film.

<Comparative Batteries 1W and 1X>

Comparative Batteries 1W and 1X were obtained by the same methods usedto obtain Sample Batteries 1A and 1E, respectively, except that a 25 μmpolyethylene-polypropylene composite film (Celgard 2300) was used inplace of the alumina particle-containing porous aramide thin film.

<Comparative Batteries 1Y through 9Y>

Comparative Batteries 1 Y through 9Y were obtained by the same methodsused to prepare Samples Batteries 1A through 9A, respectively, exceptthat artificial graphite powder was used in place of Li₄Ti₅O₁₂ as thenegative electrode active material.

<Comparative Battery 10Y>

Comparative Battery 10Y was obtained by the same methods used to prepareSample Battery 1A except that artificial graphite powder was used inplace of Li₄Ti₅O₁₂ as the negative electrode active material, and noalumina was added when preparing the alumina particle-containing porousaramide thin film.

<Comparative Battery 11Y>

Comparative Battery 11Y was obtained by the same methods used to prepareSample Battery 1A except that a 25 μm polyethylene-polypropylenecomposite film (Celgard 2300) was used in place of the aluminaparticle-containing porous aramide thin film.

<Comparative Batteries 1Z through 9Z>

Comparative Batteries 1Z through 9Z were obtained by the same methodsused to prepare Sample Batteries 1A through 9A, respectively, exceptthat LiCoO₂ (lithium cobaltate) was used in place ofLi_(1.1)Al_(0.1)Mn_(1.8)O₄ as the positive electrode active material.

<Comparative Battery 10Z>

Comparative Battery 10Z was obtained by the same methods used to prepareComparative Battery 1Z except that no alumina was added when preparingthe alumina particle-containing porous aramide thin film.

<Comparative Battery 11Z>

Comparative Battery 11Z was prepared by the same methods used to prepareComparative Battery 1Z except that a 25 μm polyethylene-polypropylenecomposite film (Celgard 2300) was used in place of the aluminaparticle-containing porous aramide thin film.

[Evaluation]

With respect to the resulting Sample Batteries and ComparativeBatteries, the output characteristics and charge transfer resistance at−18° C. were evaluated as follows. The results are shown in Tables 1through 5.

(Output Characteristics)

Break-in charge and discharge was performed twice according to thefollowing break-in charge-discharge pattern for the Sample Batteries andComparative Batteries, which were then stored for 2 days at 40° C. Theywere then charged to a battery voltage of 2.9 V (or 3.6 V or 4.2 V) at aconstant current of 1400 mA in a 25° C. environment, and then charged atconstant voltage until the electrical charge was 30 mA at that voltage.The voltage at 30 seconds during 30-second discharge was then measuredat a constant current of 16 A at a −18° C. environment. The end voltagewas selected so as to correspond to 14.4 to 10.2 V (the operating rangeof a lead battery) in the case of a serial battery assembly (4 or 5batteries). However, because this would be outside the operating voltagerange for Comparative Batteries 1W through 11W, these were charged anddischarged in the range of 4.2 V to 3.0 V, which is the normal operatingrange of a lithium ion secondary battery.

Break-In Charge-Discharge Pattern

Charge: first charged to a battery voltage of 2.9 V, 3.6 V or 4.2 Vunder constant current of 400 mA in a 25° C. environment, then chargedwith constant voltage to an electrical charge of 50 mA at the samevoltage.

Discharge: discharged to a battery voltage of 2 V at a constant currentof 400 mA in a 25° C. environment.

(Measurement of Charge Transfer Resistance)

Using the Sample Batteries and Comparative Batteries after evaluation ofbattery charge-discharge characteristics, resistance was measured by anAC impedance method under state of charge (SOC) of 2.9 V, 3.6 V or 4.2 Vat a −18° C. environment.

For the AC impedance method, a frequency response analyzer, Solartron1260 and a potentiostat/galvanostat, Solartron 1287 (both by Toyo Corp.,frequency 10 KHz to 0.01 Hz) were used. Because the time constants ofthe positive and negative plates are similar, it was not possible todistinguish whether a reduction in charge transfer resistance wasattributable to the positive plate or the negative plate.

TABLE 1 SEPARATOR POROUS THIN FILM OR POROUS THIN FILM LAYER POSITIVENEGATIVE OTHER SEPARATOR ADHESIVELY LAMINATED ON PLATE ELECTRODEELECTRODE INORGANIC PARTICLES INORGANIC SAMPLE ACTIVE ACTIVE ADDEDELECTRODE PARTICLES BINDER BATTERY MATERIAL MATERIAL FORM KIND AMOUNT(%)ATTACHED KIND KIND  1A Li_(1.1)Al_(0.1)Mn_(1.8)O₄ Li₄Ti₅O₁₂ ARAMIDEALUMINA 0.1 — — — THIN FILM (TF)  2A — — — POSITIVE ALUMINA BM-720H  3ANEGATIVE  4A ARAMIDE TF + ALUMINA 0.1 — — — PE/PP TF  5A PE/PP TF — —POSITIVE ALUMINA BM-720H  6A NEGATIVE  7A PP POSITIVE  8A NONWOVENNEGATIVE  9A ALUMINA 0.5 — — — 10A ARAMIDE TF 0.05  1BLiNi_(1/2)Mn_(1/2)O₂ ARAMIDE TF 0.1  2B — — — POSITIVE ALUMINA BM-720H 3B NEGATIVE  4B ARAMIDE TF + ALUMINA 0.1 — — — PE/PP TF  5B PE/PP TF —— POSITIVE ALUMINA BM-720H  6B NEGATIVE  7B PP POSITIVE  8B NONWOVENNEGATIVE  9B ALUMINA 0.5 — — —  1C LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ ARAMIDETF 0.1  2C — — — POSITIVE ALUMINA BM-720H  3C NEGATIVE  4C ARAMIDE TF +ALUMINA 0.1 — — — PE/PP TF  5C PE/PP TF — — POSITIVE ALUMINA BM-720H  6CNEGATIVE  7C PP POSITIVE  8C NONWOVEN NEGATIVE  9C ALUMINA 0.5 — — —  1DLi_(1.1)Mn₂O₄ ARAMIDE TF 0.1  2D — — — POSITIVE ALUMINA BM-720H  3DNEGATIVE  4D ARAMIDE TF + ALUMINA 0.1 — — — PE/PP TF  5D PE/PP TF — —POSITIVE ALUMINA BM-720H  6D NEGATIVE  7D PP POSITIVE  8D NONWOVENNEGATIVE  9D ALUMINA 0.5 — — —  1E LiNi_(2/3)Mn_(4/3)O₄ ARAMIDE TF 0.1 2E — — — POSITIVE ALUMINA BM-720H  3E NEGATIVE  4E ARAMIDE TF + ALUMINA0.1 — — — PE/PP TF  5E PE/PP TF — — POSITIVE ALUMINA BM-720H  6ENEGATIVE  7E PP POSITIVE  8E NONWOVEN NEGATIVE  9E ALUMINA 0.5 — — —EVALUATION RESULTS CHARGE TRANSFER LOW-TEMPERATURE RESISTANCE (MΩ)SAMPLE ELECTROLYTIC OUTPUT 2.9 V 3.6 V BATTERY SOLUTION CHARACTERISTICS(V) SOC SOC  1A 1.5 M LiPF₆ 1.32 60 —  2A IN 1.3 61  3A EC•MEC 1.31 62 4A MIXED 1.35 61  5A SOLVENT 1.3 62  6A (VOLUME 1.3 60  7A RATIO 1:3)1.31 61  8A 1.3 62  9A 1.32 65 10A 1.33 64  1B 1.24 62  2B 1.22 61  3B1.25 63  4B 1.21 62  5B 1.2 60  6B 1.22 61  7B 1.23 62  8B 1.24 63  9B1.22 64  1C 1.23 65  2C 1.22 62  3C 1.23 53  4C 1.24 65  5C 1.25 64  6C1.23 62  7C 1.22 63  8C 1.24 62  9C 1.25 64  1D 1.24 62  2D 1.25 63  3D1.26 62  4D 1.27 64  5D 1.24 63  6D 1.23 62  7D 1.25 61  8D 1.24 62  9D1.25 63  1E 1.51 — 77  2E 1.52 78  3E 1.5 78  4E 1.5 78  5E 1.51 77  6E1.5 77  7E 1.5 77  8E 1.51 78  9E 1.5 77

TABLE 2 SEPARATOR POROUS THIN FILM OR POROUS THIN FILM LAYER POSITIVENEGATIVE OTHER SEPARATOR ADHESIVELY LAMINATED ON PLATE ELECTRODEELECTRODE INORGANIC PARTICLES INORGANIC SAMPLE ACTIVE ACTIVE ADDEDELECTRODE PARTICLES BINDER BATTERY MATERIAL MATERIAL FORM KIND AMOUNT(%)ATTACHED KIND KIND 1F Li_(1.1)Al_(0.1)Mn_(1.8)O₄ Li₄Ti₅O₁₂ ARAMIDEALUMINA 0.1 — — — THIN FILM (TF) 2F — — — POSITIVE ALUMINA BM-720H 3FNEGATIVE 4F ARAMIDE TF + ALUMINA 0.1 — — — PE/PP TF 5F PE/PP TF — —POSITIVE ALUMINA BM-720H 6F NEGATIVE 7F PP POSITIVE 8F NONWOVEN NEGATIVE9F ALUMINA 0.5 — — — 1G ARAMIDE TF 0.1 2G — — — POSITIVE ALUMINA BM-720H3G NEGATIVE 4G ARAMIDE TF + ALUMINA 0.1 — — — PE/PP TF 5G PE/PP TF — —POSITIVE ALUMINA BM-720H 6G NEGATIVE 7G PP POSITIVE 8G NONWOVEN NEGATIVE9G ALUMINA 0.5 — — — 1H ARAMIDE TF 0.1 2H — — — POSITIVE ALUMINA BM-720H3H NEGATIVE 4H ARAMIDE TF + ALUMINA 0.1 — — — PE/PP TF 5H PE/PP TF — —POSITIVE ALUMINA BM-720H 6H NEGATIVE 7H PP POSITIVE 8H NONWOVEN NEGATIVE9H ALUMINA 0.5 — — — 1I ARAMIDE TF 0.1 2I — — — POSITIVE ALUMINA BM-720H3I NEGATIVE 4I ARAMIDE TF + ALUMINA 0.1 — — — PE/PP TF 5I PE/PP TF — —POSITIVE ALUMINA BM-720H 6I NEGATIVE 7I PP POSITIVE 8I NONWOVEN NEGATIVE9I ALUMINA 0.5 — — — 1J ARAMIDE TF 0.1 2J — — — POSITIVE ALUMINA BM-720H3J NEGATIVE 4J ARAMIDE TF + ALUMINA 0.1 — — — PE/PP TF 5J PE/PP TF — —POSITIVE ALUMINA BM-720H 6J NEGATIVE 7J PP POSITIVE 8J NONWOVEN NEGATIVE9J ALUMINA 0.5 — — — EVALUATION RESULTS CHARGE TRANSFER LOW-TEMPERATURERESISTANCE (MΩ) SAMPLE ELECTROLYTIC OUTPUT 2.9 V 3.6 V BATTERY SOLUTIONCHARACTERISTICS (V) SOC SOC 1F 1.5 M LiPF₆ 1.23 65 — 2F IN 1.25 64 3FEC•MEC 1.24 62 4F MIXED 1.24 63 5F SOLVENT 1.25 65 6F (VOLUME 1.26 64 7FRATIO 1:1) 1.25 62 8F 1.24 61 9F 1.25 62 1G 1.5 M LiPF₆ 1.19 63 2G INTMP 1.18 64 3G 1.17 65 4G 1.17 63 5G 1.16 62 6G 1.16 65 7G 1.18 62 8G1.17 65 9G 1.17 62 1H 1.5 M LiPF₆ 1.28 62 2H IN SL 1.27 62 3H 1.27 61 4H1.28 63 5H 1.29 64 6H 1.28 65 7H 1.27 63 8H 1.27 65 9H 1.27 62 1I 1.5 MLiPF₆ 1.24 62 2I IN AN 1.25 61 3I 1.24 63 4I 1.23 63 5I 1.22 62 6I 1.2563 7I 1.22 63 8I 1.24 64 9I 1.25 65 1J 1.5 M LiPF₆ 1.24 65 2J IN PN 1.2562 3J 1.24 65 4J 1.23 61 5J 1.22 63 6J 1.25 65 7J 1.22 64 8J 1.24 62 9J1.25 63

TABLE 3 SEPARATOR POROUS THIN FILM OR POROUS THIN FILM LAYER POSITIVENEGATIVE OTHER SEPARATOR ADHESIVELY LAMINATED ON PLATE ELECTRODEELECTRODE INORGANIC PARTICLES INORGANIC SAMPLE ACTIVE ACTIVE ADDEDELECTRODE PARTICLES BINDER BATTERY MATERIAL MATERIAL FORM KIND AMOUNT(%)ATTACHED KIND KIND 1K Li_(1.1)Al_(0.1)Mn_(1.8)O₄ Li₄Ti₅O₁₂ ARAMIDEALUMINA 0.1 — — — THIN FILM (TF) 2K — — — POSITIVE ALUMINA BM-720H 3KNEGATIVE 4K ARAMIDE TF + ALUMINA 0.1 — — — PE/PP TF 5K PE/PP TF — —POSITIVE ALUMINA BM-720H 6K NEGATIVE 7K PP POSITIVE 8K NONWOVEN NEGATIVE9K ALUMINA 0.5 — — — 1L ARAMIDE TF 0.1 2L — — — POSITIVE ALUMINA BM-720H3L NEGATIVE 4L ARAMIDE TF + ALUMINA 0.1 — — — PE/PP TF 5L PE/PP TF — —POSITIVE ALUMINA BM-720H 6L NEGATIVE 7L PP POSITIVE 8L NONWOVEN NEGATIVE9L ALUMINA 0.5 — — — 1M ARAMIDE TF 0.1 2M — — — POSITIVE ALUMINA BM-720H3M NEGATIVE 4M ARAMIDE TF + ALUMINA 0.1 — — — PE/PP TF 5M PE/PP TF — —POSITIVE ALUMINA BM-720H 6M NEGATIVE 7M PP POSITIVE 8M NONWOVEN NEGATIVE9M ALUMINA 0.5 — — — 1N ARAMIDE TF 0.1 2N — — — POSITIVE ALUMINA BM-720H3N NEGATIVE 4N ARAMIDE TF + ALUMINA 0.1 — — — PE/PP TF 5N PE/PP TF — —POSITIVE ALUMINA BM-720H 6N NEGATIVE 7N PP POSITIVE 8N NONWOVEN NEGATIVE9N ALUMINA 0.5 — — — 1O ARAMIDE TF 0.1 2O — — — POSITIVE ALUMINA BM-720H3O NEGATIVE 4O ARAMIDE TF + ALUMINA 0.1 — — — PE/PP TF 5O PE/PP TF — —POSITIVE ALUMINA BM-720H 6O NEGATIVE 7O PP POSITIVE 8O NONWOVEN NEGATIVE9O ALUMINA 0.5 — — — EVALUATION RESULTS CHARGE TRANSFER LOW-TEMPERATURERESISTANCE (MΩ) SAMPLE ELECTROLYTIC OUTPUT 2.9 V 3.6 V BATTERY SOLUTIONCHARACTERISTICS (V) SOC SOC 1K 1.5 M LiPF₆ 1.24 61 — 2K IN BN 1.25 62 3K1.24 63 4K 1.23 64 5K 1.22 62 6K 1.25 64 7K 1.22 65 8K 1.24 63 9K 1.2562 1L 1.5 M LiPF₆ 1.24 63 2L IN 1.25 64 3L FETFPE 1.24 65 4L 1.23 64 5L1.22 66 6L 1.25 65 7L 1.22 62 8L 1.24 64 9L 1.25 62 1M 1.5 M LiPF₆ 1.2465 2M IN 1.25 66 3M TFPDFME 1.24 63 4M 1.23 62 5M 1.22 61 6M 1.25 62 7M1.22 64 8M 1.24 62 9M 1.25 65 1N 1.5 M LiPF₆ 1.24 61 2N IN MDFA 1.25 623N 1.24 65 4N 1.23 66 5N 1.22 63 6N 1.25 64 7N 1.22 64 8N 1.24 62 9N1.25 65 1O 1.5 M LiPF₆ 1.24 62 2O IN EDFA 1.25 64 3O 1.24 61 4O 1.23 635O 1.22 62 6O 1.25 61 7O 1.22 64 8O 1.24 65 9O 1.25 63

TABLE 4 SEPARATOR POROUS THIN FILM OR POROUS THIN FILM LAYER POSITIVENEGATIVE OTHER SEPARATOR ADHESIVELY LAMINATED ON PLATE ELECTRODEELECTRODE INORGANIC PARTICLES INORGANIC SAMPLE ACTIVE ACTIVE ADDEDELECTRODE PARTICLES BINDER BATTERY MATERIAL MATERIAL FORM KIND AMOUNT(%)ATTACHED KIND KIND 1P Li_(1.1)Al_(0.1)Mn_(1.8)O₄ Li₄Ti₅O₁₂ ARAMIDEALUMINA 0.1 — — — THIN FILM (TF) 2P — — — POSITIVE ALUMINA BM-720H 3PNEGATIVE 4P ARAMIDE TF + ALUMINA 0.1 — — — PE/PP TF 5P PE/PP TF — —POSITIVE ALUMINA BM-720H 6P NEGATIVE 7P PP POSITIVE 8P NONWOVEN NEGATIVE9P ALUMINA 0.5 — — — 1Q ARAMIDE TF 0.1 2Q — — — POSITIVE ALUMINA BM-720H3Q NEGATIVE 4Q ARAMIDE TF + ALUMINA 0.1 — — — PE/PP TF 5Q PE/PP TF — —POSITIVE ALUMINA BM-720H 6Q NEGATIVE 7Q PP POSITIVE 8Q NONWOVEN NEGATIVE9Q ALUMINA 0.5 — — — 1R ARAMIDE TF MAGNESIA 0.1 2R — — — POSITIVEMAGNESIA BM-720H 3R NEGATIVE 4R ARAMIDE TF + MAGNESIA 0.1 — — — PE/PP TF5R PE/PP TF — — POSITIVE MAGNESIA BM-720H 6R NEGATIVE 7R PP POSITIVE 8RNONWOVEN NEGATIVE 9R MAGNESIA 0.5 — — — 1S ARAMIDE TF GLASS 0.1 POWDER2S — — — POSITIVE GLASS BM-720H POWDER 3S NEGATIVE 4S ARAMIDE TF + GLASS0.1 — — — PE/PP TF POWDER 5S PE/PP TF — — POSITIVE GLASS BM-720H POWDER6S NEGATIVE 7S PP POSITIVE 8S NONWOVEN NEGATIVE 9S GLASS 0.5 — — —POWDER 1T ARAMIDE TF MICA 0.1 WHISKERS 2T — — — POSITIVE MICA BM-720HWHISKERS 3T NEGATIVE 4T ARAMIDE TF + MICA 0.1 — — — PE/PP TF WHISKERS 5TPE/PP TF — — POSITIVE MICA BM-720H WHISKERS 6T NEGATIVE 7T PP POSITIVE8T NONWOVEN NEGATIVE 9T MICA 0.5 — — — WHISKERS EVALUATION RESULTSCHARGE TRANSFER LOW-TEMPERATURE RESISTANCE (MΩ) SAMPLE ELECTROLYTICOUTPUT 2.9 V 3.6 V BATTERY SOLUTION CHARACTERISTICS (V) SOC SOC 1P 1.5 MLiPF₆ 1.24 62 — 2P IN ETFEC 1.25 65 3P 1.24 64 4P 1.23 62 5P 1.22 66 6P1.25 65 7P 1.22 64 8P 1.24 62 9P 1.25 63 1Q 1.5 M LiPF₆ 1.24 62 2Q INDTFEC 1.25 64 3Q 1.24 65 4Q 1.23 62 5Q 1.22 66 6Q 1.25 63 7Q 1.22 61 8Q1.24 62 9Q 1.25 64 1R 1.5 M LiPF₆ 1.22 63 2R IN EC•MEC 1.23 63 3R MIXED1.24 62 4R SOLVENT 1.22 64 5R (VOLUME 1.24 64 6R RATIO 1:3) 1.22 65 7R1.23 65 8R 1.22 65 9R 1.25 65 1S 1.5 M LiPF₆ 1.21 64 2S IN EC•MEC 1.2262 3S MIXED 1.23 64 4S SOLVENT 1.23 63 5S (VOLUME 1.24 64 6S RATIO 1:3)1.23 64 7S 1.22 64 8S 1.23 63 9S 1.24 65 1T 1.5 M LiPF₆ 1.23 63 2T INEC•MEC 1.23 61 3T MIXED 1.22 64 4T SOLVENT 1.22 62 5T (VOLUME 1.23 63 6TRATIO 1:3) 1.24 64 7T 1.22 64 8T 1.24 65 9T 1.23 62

TABLE 5 SEPARATOR POROUS THIN FILM OR POROUS THIN FILM LAYER POSITIVENEGATIVE OTHER SEPARATOR ADHESIVELY LAMINATED ON PLATE COMPAR- ELECTRODEELECTRODE INORGANIC PARTICLES INORGANIC ATIVE ACTIVE ACTIVE ADDEDELECTRODE PARTICLES BINDER BATTERY MATERIAL MATERIAL FORM KIND AMOUNT(%)ATTACHED KIND KIND  1U Li_(1.1)Al_(0.1)Mn_(1.8)O₄ Li₄Ti₅O₁₂ ARAMIDE — —— — —  1V LiNi_(2/3)Mn_(4/3)O₄ THIN FILM(TF)  1WLi_(1.1)Al_(0.1)Mn_(1.8)O₄ POLYETHYLENE +  1X LiNi_(2/3)Mn_(4/3)O₄POLYPROPYLENE  1Y Li_(1.1)Al_(0.1)Mn_(1.8)O₄ ARTIFICIAL ARAMIDE TFALUMINA 0.1  2Y GRAPHITE — — — POSITIVE ALUMINA BM-720H  3Y NEGATIVE  4YARAMIDE TF + ALUMINA 0.1 — — — PE/PP TF  5Y PE/PP TF — — POSITIVEALUMINA BM-720H  6Y NEGATIVE  7Y PP POSITIVE  8Y NONWOVEN NEGATIVE  9YALUMINA 0.5 — — — 10Y ARAMIDE TF — — 11Y PE/PP TF  1Z LiCoO₂ Li₄Ti₅O₁₂ARAMIDE TF ALUMINA 0.1  2Z — — — POSITIVE ALUMINA BM-720H  3Z NEGATIVE 4Z ARAMIDE TF + ALUMINA 0.1 — — — PE/PP TF  5Z PE/PP TF — — POSITIVEALUMINA BM-720H  6Z NEGATIVE  7Z PP POSITIVE  8Z NONWOVEN NEGATIVE  9ZALUMINA 0.5 — — — 10Z ARAMIDE TF — — 11Z PE/PP TF EVALUATION RESULTSCOMPAR- CHARGE TRANSFER ATIVE LOW-TEMPERATURE RESISTANCE (MΩ) SAMPLEELECTROLYTIC OUTPUT 2.9 V 3.6 V 4.2 V BATTERY SOLUTION CHARACTERISTICS(V) SOC SOC SOC  1U 1.5 M LiPF₆ 0.9 82 — —  1V IN EC•MEC 1.2 — 80  1WMIXED 0.87 81 —  1X SOLVENT 1.21 — 80  1Y (VOLUME 0.95 80 — 82  2Y RATIO1:3) 1.2 85 83  3Y 1.22 84 84  4Y 1.23 82 82  5Y 1.24 85 85  6Y 1.25 8484  7Y 1.22 82 82  8Y 1.24 83 83  9Y 1.22 84 84 10Y 1.24 87 85 11Y 1.2581 84  1Z 0.95 80  2Z 0.95 81  3Z 0.94 80  4Z 0.93 81  5Z 0.94 82  6Z0.94 81  7Z 0.95 80  8Z 0.94 82  9Z 0.95 81 10Z 0.89 80 11Z 0.89 81

As found from Tables 1 through 5, Sample Batteries 1A through 9A, 1Bthrough 9B, 1C through 9C, 1D through 9D, 1E through 9E, 1F through 9F,1G through 9G, 1H through 9H, 1I through 9I, 1J through 9J, 1K through9K, 1L through 9L, 1M through 9M, 1N through 9N, 1O through 9O, 1Pthrough 9P, 1Q through 9Q, 1R through 9R, 1S through 9S and 1T through9T showed a tendency to decrease the values of charge transferresistance and increase the maintenance voltage during high-ratedischarge in a low-temperature environment, compared to ComparativeBatteries 1U, 1V, 1W, 1X, 1Y through 11Y and 1Z through 11Z lacking inthe aforementioned configuration.

In the case of Sample Battery 10A in which the added amount of inorganicparticles (alumina) was 0.05 mass % being lower than 0.1 mass %, thecharge transfer resistance was only slightly lower than that ofComparative Battery 1U, and the maintenance voltage during high-ratedischarge was about the same as that of Comparative Battery 1U.

One aspect of the present invention is a nonaqueous electrolytesecondary battery provided with a nonaqueous electrolyte and anelectrode assembly comprising a positive electrode having a positiveelectrode active material, a negative electrode having a negativeelectrode active material and a separator interposed between thepositive and negative electrodes, wherein the positive electrode activematerial contains a lithium-manganese composite oxide containing lithiumand manganese as constituent elements, the negative electrode activematerial contains a lithium-titanium composite oxide containing lithiumand titanium as constituent elements, and the separator containsinorganic particles.

The immediate reason why the output characteristics in low-temperatureenvironments are improved by means of this configuration is unknown atpresent. As a result of various investigations, however, a phenomenonhas been found that suggests that it is influenced by the size of thecharge transfer resistance in the state of charge in the positive ornegative electrode, as explained below.

In a lithium-ion secondary battery using a lithium-manganese compositeoxide as the positive electrode active material, manganese ions areeluted into the nonaqueous electrolyte from the positive electrodeactive material during charge and discharge. Under these circumstances,when a lithium-titanium composite oxide is used as the negativeelectrode active material, the manganese remains as manganese ions inthe nonaqueous electrolyte rather than being deposited on the negativeelectrode surface. This happens because the deposition potential of themanganese is lower than the oxidation-reduction potential of thelithium-titanium composite oxide. The present inventors discovered thatwhen manganese ions are present in the nonaqueous electrolyte of thebattery, the charge transfer resistance of the electrodes in a chargedstate is specifically reduced and the output characteristics at lowtemperatures are improved when the separator contains inorganicparticles. When a carbon material is used as the negative electrodeactive material, on the other hand, the manganese is deposited on thenegative electrode surface, and very few manganese ions remain in thenonaqueous electrolyte. This happens because the deposition potential ofthe manganese is higher than the oxidation-reduction potential of thecarbon material. In this case, even if the separator contains inorganicparticles, the charge transfer resistance of the electrode in a 4.2 Vstate of charge was not altered, and the output characteristics in lowtemperature environments were only slightly improved.

In a nonaqueous electrolyte secondary battery using lithium cobaltate asthe positive electrode active material and a lithium-titanium compositeoxide as the negative electrode active material, including inorganicparticles in the separator made no difference in the charge transferresistance of the electrode in a 2.9 V state of charge, and onlyslightly improved the output characteristics in low-temperatureenvironments. This is attributed to the absence of manganese ions in theelectrolyte.

It can be inferred from the above phenomena that in a nonaqueouselectrolyte secondary battery using a lithium-manganese composite oxideas the positive electrode active material and a lithium-titaniumcomposite oxide as the negative electrode active material, the mechanismby which the output characteristics in low-temperature environments areimproved when the separator contains inorganic particles is consideredas follows. Some of the manganese ions eluted in the electrolyte areadsorbed by inorganic particles on the surface of the separator, and thecharacteristics of the electrode surface are altered by the presence ofthese inorganic particles in the vicinity of the electrodes, leading toan increase in the transfer speed of the lithium ions near theelectrodes in low-temperature environments.

The separator is preferably a porous thin film layer containing theinorganic particles that is formed on the surface of the positiveelectrode and/or the negative electrode, and specifically, the porousthin film layer is preferably a thin film layer that is formed bybinding the inorganic particles together with a binder, from thestandpoint of improving shape stability of the separator.

It is desirable that the organic particles be organic oxide particles,and specifically alumina and/or magnesia particles in terms of abilityto adsorb manganese ions.

From the standpoint of reducing the weight and cost of the battery, itis desirable that the positive electrode comprises a positive electrodecurrent collector and a positive electrode mixture layer containing thepositive electrode active material formed on the surface of the positiveelectrode current collector, that the negative electrode comprises anegative electrode current collector and a negative electrode mixturelayer containing the negative electrode active material formed on thesurface of the negative electrode current collector, and that thepositive electrode current collector and the negative electrode currentcollector are made of an aluminum-based metal.

It is desirable from the standpoint of cost, ability to dissolve theelectrolyte, safety and the like that the nonaqueous electrolytecontains an electrolyte dissolved in a nonaqueous solvent, and that thenonaqueous solvent contains at least one selected from the groupconsisting of propylene carbonate, trimethylphosphate, sulfolane,acetonitrile, propionitrile, butyronitrile, fluorinated ether,fluorinated carboxylic acid ester, and fluorinated ethylene carbonate.

1. A nonaqueous electrolyte secondary battery provided with a nonaqueouselectrolyte and an electrode assembly comprising a positive electrodehaving a positive electrode active material, a negative electrode havinga negative electrode active material and a separator interposed betweenthe positive and negative electrodes, wherein the positive electrodeactive material contains a lithium-manganese composite oxide containinglithium and manganese as constituent elements, the negative electrodeactive material contains a lithium-titanium composite oxide containinglithium and titanium as constituent elements, and the separator containsinorganic particles, the lithium-titanium composite oxide is Li₄Ti₅O₁₂,and the inorganic particles are inorganic oxide particles of at leastone kind selected from alumina and magnesia.
 2. The nonaqueouselectrolyte secondary battery according to claim 1, wherein theseparator is a porous thin film layer containing the inorganicparticles, and the porous thin film layer is formed on a surface of thepositive electrode and/or the negative electrode.
 3. The nonaqueouselectrolyte secondary battery according to claim 2, wherein the porousthin film layer containing the inorganic particles is a thin film layerformed by binding the inorganic particles with a binder. 4-5. (canceled)6. The nonaqueous electrolyte secondary battery according to claim 1,wherein the positive electrode comprises a positive electrode currentcollector and a positive electrode mixture layer containing the positiveelectrode active material formed on the surface of the positiveelectrode current collector, the negative electrode comprises a negativeelectrode current collector and a negative electrode mixture layercontaining the negative electrode active material formed on the surfaceof the negative electrode current collector, and the positive electrodecurrent collector and the negative electrode current collector are madeof an aluminum-based metal.
 7. The nonaqueous electrolyte secondarybattery according to claim 1, wherein the nonaqueous electrolytecontains an electrolyte dissolved in a nonaqueous solvent, and thenonaqueous solvent contains at least one selected from the groupconsisting of propylene carbonate, trimethylphosphate, sulfolane,acetonitrile, propionitrile, butyronitrile, fluorinated ether,fluorinated carboxylic acid ester, and fluorinated ethylene carbonate.